114 



EARTHQUAKES. 



The Swing of Buildings. — The distance through 

 which buildings are moved at the time of an earthquake 

 depends partly on their construction and partly on the 

 extent, nature, and duration of the movement com- 

 municated to them at their foundations. By violent 

 shocks buildings may be completely overthrown. In the 

 case of small earthquakes, the upper portion of a house 

 may frequently move through a much greater distance 

 than the ground at its foundation. For instance, during 



Fig. 23. — ^Webber House, San Francisco. Oct. 21, 1868. 



the Yokohama earthquake of February, 1880, when the 

 maximum amplitude of the earth's motion was probably 

 under | of an inch, from the slow swing of long Japanese 

 pictures, from three to six feet in length, which oscillated 

 backwards and forwards on the wall, it is very probable 

 that the extent through which the upper portion of 

 houses moved was very considerable. In some instances 

 these pictures seem to have swung as much as two feet, 

 and from the manner in which they swung they evi- 

 dently synchronised with the natural swing of the house. 



